1. Field of the Invention
The present invention relates to a side-light type spread illuminating apparatus having a light guide plate provided with a light output portion and a light input end face. A tight source is disposed on the light input end face so as to emit planar illumination light from the light output portion.
2. Description of the Related Art
For illumination units of a liquid crystal display panel, side-light type spread illuminating apparatuses (backlight) have been popularly used. In the apparatuses, light-emitting diodes (LEDs), being small but securing excellent environmental feasibilities, are arranged along the side end face of a light guide plate. These apparatuses have been widely employed in the field of miniaturized portable information apparatuses such as a mobile phone, etc.
In recent, for coping with need that makes the miniaturized portable information apparatuses to be further thinned, a light guide plate is configured to have an inclination portion between the light input surface and the light output portion. With formation of the inclination, the thickness of the light guide plate gradually decreases as moving away from the side end face (hereinafter, referred to as a light input surface) on which LEDs are arranged. For applying such a light guide plate, it is possible to thin the light output portion of the light guide plate regardless of the thickness of the LEDs.
In this type of the spread illuminating apparatus, the LEDs are typically arranged to face the light input surface of the light guide plate while being mounted on a rectangle circuit board. In this case, a front portion of the circuit board is abutted and fixed to the vicinity of the light input surface of the light guide plate (including an inclined surface of the inclination portion) so that the LED is positioned at the light guide plate.
In related arts, in such a type of the spread illuminating apparatus, when light is emitted from the LEDs and introduced into the light guide plate, some light is absorbed in the circuit board fixed to the inclined surface when reflected on the inclined surface. Further, as explained, since the circuit board is fixed to the inclined surface of the light guide plate, it becomes difficult for the light-emitting surface of the LED to face the light input surface of the light guide plate in parallel. A part of light that has been emitted from the light-emitting surface of the LED thus may externally leak without being introduced into the light input surface of the light guide plate. As a result, luminance of the illumination light may be degraded.
In order to solve the aforementioned problems and improve luminance of the illumination light, the applicant has proposed a spread illuminating apparatus described hereinbelow (see JP 2011-96523 A). FIG. 6 is an exploded plan view illustrating one example of the main parts of a spread illuminating apparatus 100. FIG. 7 is a cross-sectional view taken along a line A-A when the spread illuminating apparatus 100 is assembled. FIG. 8 is a plan view illustrating an exemplary flexible printed circuit board (hereinafter, referred to as a FPC) 131 in the spread illuminating apparatus 100 when viewed from the mount surface 131a side on which an LED 111, etc. are mounted.
In the spread illuminating apparatus 100, the light guide plate 121 includes: a light input portion 126 formed facing the light input surface 122; an inclination portion 127 formed continuously with the light input portion 126, the inclination portion 127 being configured that its thickness gradually decreases toward a front direction (meaning moving away from the light input surface 122); and a light output portion 128 formed in front of the inclination portion 127 and emits light, guided from the LED 111 toward the inclination portion 127, from the light output surface 125. In addition, the inclination portion 127 formed near the light input surface 122 of the light guide plate 121 includes a plurality of pedestals 129 in some areas except the front of the LED 111. The top surface 129a of each pedestal 129 is approximately perpendicular to the light input surface 122 of the light guide plate 121. The FPC 131 is fixed to the light guide plate 121 by bonding a part of the mount surface 131a to the top surface 129a of the pedestal 129 using a double-sided tape 140.
Furthermore, in the spread illuminating apparatus 100, the light guide plate 121 has a plurality of claw portions 130 that are separated from each other and protrude from the light input surface 122 to a rear direction (meaning opposite to the front direction). The top surface 130a of the claw portion 130 is approximately flush with the top surface 126a of the light input portion 126 and the top surface 129a of the pedestal 129. A part of the mount surface 131a of the FPC 131 is also bonded to the top surface 130a of the claw portion 130 using the double-sided tape 140.
In this configuration of the spread illuminating apparatus 100, while the FPC 131 is fixed to the light guide plate 121, the light-emitting surface 112 of the LED 111 faces the light input surface 122 of the light guide plate 121 approximately in parallel to each other. Therefore, it is possible to efficiently introduce light emitted from the light-emitting surface 112 of the LED 111 to the inside of the light guide plate 121 with no leakage light. In this manner, the spread illuminating apparatus 100 could achieve high luminance of the illumination light while solving the aforementioned problems.
Furthermore, in the spread illuminating apparatus 100, since the FPC 131 is fixed to the light guide plate 121, a gap would be present between the inclined surface 127a in front of the LED 111 and the mount surface 131a of the FPC 131. Therefore, light introduced into the light guide plate 121 and reflected on the inclined surface 127a can be suppressed from being absorbed into the FPC 131, being possible to achieve high luminance of the illumination light.